Brake system comprising a clutch shiftable by the brake pedal for disengaging the drive device from the piston-cylinder unit

ABSTRACT

The invention relates to a brake system, comprising at least one piston-cylinder unit for producing a pressure in at least one working chamber, the working chamber being connected to at least one wheel brake via at least one hydraulic line, and the brake system comprising at least one drive device and an actuating device, particularly in the form of a brake pedal, and the drive device during normal operation acting on the at least one first piston of the piston-cylinder unit for building pressure and reducing pressure by way of a first force transmission means, and in the event of failure of the drive device the actuating device acting mechanically on the piston by way of a second force transmission means, wherein the adjustment of the second force transmission means disengages the connection between the first force transmission means and the piston by means of the actuating device.

The present invention relates to a brake system, comprising at least onepiston-cylinder unit for producing a pressure in at least one workingchamber, the working chamber being connected to at least one wheel brakevia at least one hydraulic line, and the brake system comprising atleast one drive device and an actuating device, particularly in the formof a brake pedal, and the drive device during normal operation acting onthe at least one first piston of the piston-cylinder unit for buildingpressure and reducing pressure by way of a first force transmissionmeans, and in the event of failure of the drive device the actuatingdevice acting mechanically on the piston by way of a second forcetransmission means.

STATE OF THE ART

With brake systems there is a trend towards replacing the vacuum servobrake with a hydraulic or electromotive servo brake.

A version of an electromotive servo brake is described in DE 10 2004 050103 A1. Here the pressure modulation takes place in a separate unit. Theelectromotive boost is provided via a force sensor which via theelectromotor with spindle drive delivers the desired boost to thepiston. The spindle acts on the carrier in order to build pressure,damping elements being inserted between the spindle and the carrier.Return of the carrier takes place by means of the pressure forces of themain brake cylinder and its return spring (not shown). In the event offailure of the motor drive the brake pedal acts via the carrier directlyon the piston.

In DE 10 2005 018 649 an electromotive servo brake is also described,which through corresponding piston control by means of solenoid valvesapart from the servo braking also carries out the pressure modulationfor ABS/ESP. Here the main brake cylinder piston is directly connectedto the motor drive. This is necessary for rapid pressure building at lowpressures, since here the return force from the brake pressure andsprings is too low. In the event of failure of the motor a specialclutch is provided for the spindle nut which in the event of such amotor failure releases this so that the pedal force can be exerteddirectly on the main brake cylinder piston through correspondingtransmission members. This solution is expensive and requires a largeinstallation space.

DE 10 2006 050 277 likewise provides for step or annular pistons for anelectromotive servo brake. The outer piston is connected directly withthe spindle drive and together with the motor brings about the servobraking and the pressure modulation. With this solution, in the event offailure of the motor drive, the inner piston with the transmissionelements is likewise connected with the brake pedal, so that in thiscase sufficient braking effect can be achieved. The problem with thissolution is the piston seal, in particular at small piston diameterswhich are precisely what are preferred for this system. In addition, thesmaller piston, because of the smaller volume displacement isdisadvantageous compared with larger so-called floating pistons, sinceat high brake pressures it comes up against the small piston and withdiffering brake pressures.

PROBLEM FOR THE INVENTION

The problem for the present invention is to provide a brake system inwhich, in the event of a failure of the drive unit a pressure in thebrake cylinder by means of an actuating device, particularly in the formof a brake pedal, can be built independently of the drive unit.

SOLUTION TO THE PROBLEM

According to the invention this problem is solved by a brake system withthe features of claim 1 and the features of the subclaims.

The invention is based on the concept of providing a first and a secondforce transmission means. Here the first force transmission means isdriven by the drive device and in particular by an electromotive drivein the form of a spindle. The second force transmission means in theevent of a failure of the actuating device, in particular in the form ofa brake pedal, then moves and adjusts the piston, at the same time adecoupling of the form-fit that in normal operation exists between thefirst force transmission means and the piston takes place through thesecond force transmission means. In normal operation, in which thepiston is adjusted by the drive device to build up or reduce pressure,according to the invention the form-fit between the piston and the firstforce transmission means is ensured through the second forcetransmission means, which is adjusted by the drive device along with thepiston. If the drive fails and a braking effect is needed, through thebrake pedal a force can be exerted on the second force transmissionmeans, as a result of which this is adjusted relative to the piston andthe first force transmission means in the direction of the pistonagainst a spring resistance. Through this relative movement the securityof the form-fit is removed. The form-fit is thus decoupled and thepiston can through the second force transmission means be adjusted forpressure building free from the drive device.

In order that in normal operation the clutch remains engaged, that is tosay that the form-fit is ensured, a spring pushes the second forcetransmission means into a first engaging position. In this position orrelative position of the piston and the two force transmission means toeach other, the coupling element is held securely in its form-fitcreating position.

It is an advantage if the clutch described above is arranged in theimmediate vicinity of the piston. It is particularly advantageous if thefirst and second force transmission means rest by their ends in a,particularly bowl-shaped recess of the piston, which is turned away fromthe working chamber of the piston-cylinder unit. Here at least onecoupling element is supported so that it can shift radially to thecylinder axis on the piston or a part secured thereto, in particular abush. Depending of the position of the two force transmission meansrelative to each other and to the piston, the coupling element isadjusted so that it either creates the form-fit between the piston andthe first force transmission means or disengages the piston from thesecond force transmission means and thus from the drive.

Here the first force transmission means encompasses with its bowl-shapedface the bush, in which the at least one coupling element is supported,and which in turn is part of the piston or is secured to this. The freeend of the second force transmission means is enclosed in the bush. Areturn spring is also arranged in the bush, and this pushes the secondforce transmission means into the first position ensuring the form-fit.Radial windows of the bush support at least one coupling element in aradially displaceable manner, which through guide curves of the twoforce transmission means is moveable in a recess of the respective otherforce transmission means. Roll barrels or balls are advantageously usedhere as coupling elements in order to minimise friction. The secondforce transmission means is encompassed in the first force transmissionmeans in a moveable manner.

The recesses in the two force transmission means are in their simplestfrom annular grooves, the sides of the grooves being in the form ofguide curves, so that where there is a relative movement the at leastone coupling element is adjusted radially.

The use of roll barrels is very safe, cost-effective and compact. As acomponent of the push-rod and thus of the main brake cylinder these canbe easily exchanged without the need to dismantle the entire unit. Inaddition the operation of the clutch when in service can be easilydiagnosed by a comparison of the pedal position encoder and the pressuretransducer when the motor is switched on and off.

In a preferred embodiment of the inventive brake system the first and/orsecond force transmission means is supported in a moveable and/orrotating manner on the piston or in a recess on the piston. Here thesecond force transmission means is in particular in the form of a rodand is supported in the second force transmission means in a moveablemanner.

The invention is described in more detail in the following with the helpof drawings.

They show as follows:

FIG. 1: a schematic representation of the inventive brake system;

FIG. 2: an extract drawing of the part of the inventive brake systemencompassing the clutch;

FIG. 3: a detailed representation of the inventive clutch.

FIG. 1 shows an integrated servo brake with an electric motor 1 withassociated rotor 1 a, which drives the spindle nut 2. The push-rodpiston 3 is arranged in a moveable manner in the tandem main cylinder 4.The clutch 14 then acts between the piston 3 and the spindle 2 only ifthe drive 1 is intact.

The clutch itself and the connection between piston 3, spindle 2 and thepedal plunger 5 which releases this or which in the event of a failuredisengages the clutch is only shown schematically in FIG. 1 and isexplained in detail using FIG. 2.

In normal operation, activation of the brake pedal 10 is detected viathe pedal movement sensor 11 and via the motor 1 with spindle drive 5 ofthe push-rod piston 3 the building or reduction of pressure is caused.The function of pressure building and reduction is already sufficientlyknown from the documents described in this application as the state ofthe art. In this regard full reference is made to these documents. Bymeans of the piston-cylinder unit 4 the pressure building and reductionis brought about with the valves 13 in multiplex mode for the individualwheel brakes(not shown) via the electromotor 1. Regulation takes placeby means of a comparison between the sensor 15 and the pressure sensor12. The pedal reaction is generated via the path simulator 8. In orderthat the pedal path is free from reaction of the pressure control piston3, a small amount of free path s, as is also used in any vacuum servobrake, is used in order to take account of the slight start-up delay ofthe electromotor. The free path can also be created at least in part inthe clutch 14 itself.

The path simulator 8 is integrated in housing 8 along with an adaptivenon-working stroke circuit from DE 10 2006 059 840.7. If theelectromotor 1 is intact, this moveable housing is blocked from movingby the electromagnetic path simulator lock 9. In the event of failure ofthe drive 1 the brake pedal 10 with known transmission element andcoupling element 6 acts on the pedal plunger 5 and this in turn via theclutch 14 on the pressure control piston 3.

The spindle 2 is also understood to be the first force transmissionmeans, via which from the drive 1 a force can be transferred to thepiston 3 both for pressure building (the piston is displaced to theleft), and for pressure reduction, the piston also being displaced tothe left.

The pedal plunger is also understood to be the second force transmissionmeans, via which a force can be transferred from the brake pedal 10 tothe piston 3. In this way the pedal movement acts directly on the tandemmain cylinder 4.

Through the path simulator 8 and the non-working stroke s, when themotor is intact the pedal movement is disengaged from the pistonmovement.

Pressure modulation for ABS/ESP takes place by corresponding motorcontrol and piston movement in so-called multiplex mode, in which thecontrol valves 13 are switched alternately according to the necessarypressure level in relation to the control algorithm to pressurebuilding, reduction or maintenance. The pressure sensor allows thecorresponding pressure level to be detected.

Since the clutch is only shifted in emergency mode, which as a rulerarely arises, but the operation of which is crucial in the event ofmalfunction, it is recommended that the ability of the clutch to shiftis diagnosed in order to exclude any possibility of jamming. A diagnosisof the clutch 14 can be carried out, inter alia, for example if when thevehicle is started up or during vehicle acceleration phases of theelectromotor 1 the spindle 2 moves from the starting position shown inFIG. 2 in the direction of the passenger compartment in the oppositedirection to the pedal stroke direction, that is to say to the right.Since the pedal in the direction of the driver has a stop, not shown,the immobilised pedal plunger 5 immobilised as a result plunges into thespindle 2 and displaces the clutch plunger 16 relative to the spindle 2.If the clutch 14 is operating perfectly it is opened in the mannerdescribed and the motor can displace the spindle 2 further than the freepath s available in the clutch. The spindle travel can be detected viathe angle sensor 15. If the clutch 14 should jam, the spindle afterreturning through the free travel s comes up against the stop and themotor current increases correspondingly sharply.

FIG. 2 shows the coupling of the spindle 2 with the piston 3. The clutch14 is integrated into an in particular bowl-shaped recess 3 a of thepush-rod piston 3 arranged on the face turned away from the workingchambers of the tandem main brake cylinder 4. The basic elements of themain brake cylinder 4 will not be described as these are generallyknown. The piston 3 has a form-fit connection with the spherical bushing17, which incorporates several balls 18 or if necessary cylindrical rollbodies.

Within the bushing 17 the clutch plunger 16 is supported, which isconnected with the end of the pedal plunger 5. The clutch plunger 16 isreturned via a spring 19 to a stop 17 a of spherical bushing to aninitial position. The top half of the drawing shows the clutch 14 in theengaged state. The spindle 2 acts to build pressure via compensatingdiscs 20 directly on the piston 3. During pressure reduction the spindle2 acts via a hemispherical head 2 a on the balls 18, the inward radialmovement of which is prevented by corresponding ball tracks 16 a in theclutch plunger 16. The ball tracks 16 a thus act as blocking surfaces,which prevent the opening of the clutch if pressure is applied to thepedal plunger other than through the brake pedal 10. In this way innormal operation a form-fit between spindle 2 and piston 3 is achieved,which allows a rapid return of the piston 3 for pressure reduction bymeans of the electromotor 1. In normal operation no force is transmittedto the pedal plunger 5 by the described construction of the pathsimulator with stop 9.

If, as described, the motor drive fails, through the movement of thehousing 8 with the brake pedal 10 the pedal plunger 5 moves, which inturn acts on the clutch plunger 16. After travelling the free path 7 andcompressing the spring 19 the clutch plunger 16 acts on the piston 3.This takes the spherical bushing 17 with it, as a result of which theballs 18 via the hemispherical head or guide curve 2 a are pushedinwards into the recess 16 b of the clutch plunger 16. This breaks theform-fit between piston 3 and spindle 2 and the clutch is open. Thepiston 3 can now be adjusted independently of the drive via the brakepedal for pressure building. In the spherical bushing 16 insets 21 arecreated in order that the balls do not fall out when the cylinder 4 isassembled or stripped out.

The contact surfaces between spindle 2 and ball 18 or ball and clutchplunger 16 have a hemispherical shape, so that linear contact takesplace and the surface pressures are correspondingly reduced.

The clutch plunger 16 is secured against rotation to the sphericalbushing 17. To this end the ball tracks 16 a are preferably designed insuch a way that they protrude into the recesses 16 b, such that theclutch is no longer operative.

FIG. 3 shows an enlarged extract drawing showing the parts. essential tothe clutch.

List of References

1 Electromotor

1 a Rotor with spindle nut

2 Spindle

2 a Guide curve or hemispherical head

2 b Recess

3 Pressure control piston

3 a Bowl-shaped recess

4 Tandem main brake cylinder

5 Pedal plunger

6 Coupling element with brake pedal

7 Free path

8 Path simulator with adaptive free travel shifting

9 Path simulator stop

10 Brake pedal

11 Pedal movement sensor

12 Pressure sensor

13 Control valves

14 Clutch

15 Rotational angle sensor

16 Clutch plunger

16 a Ball tracks

16 b Recess

16 c Guide curve

17 Spherical bushing

17 a Stop in spherical bushing

18 Ball

19 Return spring

20 Compensating discs

21 Inset

1. A brake system, comprising at least one piston-cylinder unit forproducing a pressure in at least one working chamber, the workingchamber being connected to at least one wheel brake via at least onehydraulic line, and the brake system comprising at least one drivedevice and an actuating device, and wherein the drive device duringnormal operation is configured to act on the at least one first pistonof the piston-cylinder unit for building pressure and reducing pressureby way of a first force transmission means, and in the event of failureof the drive device the actuating device is configured to act actingmechanically on the piston by way of a second force transmission means,wherein, characterised in that adjustment of the second forcetransmission means disengages the connection between the first forcetransmission means and the piston by means of the actuating device. 2.The brake system according to claim 1, wherein in normal operation thefirst force transmission means is configured for exerting a force on thepiston directed along the cylinder axis, and has a connection with thepiston.
 3. The brake system according to claim 2, wherein the secondforce transmission means separates the connection in the event offailure, particularly by releasing a stop means.
 4. The brake systemaccording to claim 1, further comprising a clutch arranged between thepiston and the first force transmission means, wherein the second forcetransmission means is configured to operate the clutch.
 5. The brakesystem according to claim 4, wherein the piston can be moved back andforth by the drive device in the cylinder, and wherein in the event of afailure of the drive device a movement forced by the actuating device ofthe second force transmission means relative to the piston, particularlytowards the piston, open the clutch and the piston by means of theactuating device, and wherein the second force transmission means isadjustable for building pressure independently of the drive device. 6.The brake system according to claim 4, wherein the first and/or thesecond force transmission means can be shifted and/or rotated on thepiston or is/are supported in a recess of the piston, and wherein thesecond force transmission means is forced by means of the pressure of aspring in the direction of a first position and actuating device and canbe adjusted against the spring pressure to a second position relative tothe piston, wherein in the first position the second force transmissionmeans is configured to ensure the connection between first forcetransmission means and piston, and wherein in the second position or anarea between the first and second position, the second forcetransmission means is configured to separate or release the connection,wherein in the first position at least one coupling element is supportedby the piston and is held by the second force transmission means atleast partially in a recess of the first force transmission means tocreate a form-fit.
 7. (canceled)
 8. The brake system according to claim6, wherein in the second position the at least one coupling element isenclosed in a recess of the second force transmission means and does notcreate a form-fit between the first force transmission means and piston,wherein the at least one coupling element is enclosed in a radiallymoveable manner in a spherical bushing formed on or secured to thepiston.
 9. The brake system according to claim 8, wherein the first andsecond force transmission means have guide curves, which when the firstor second force transmission means moves relative to the support part,are adapted to push the at least one coupling element out from its ownrecess and into the recess of the respective other force transmissionmeans. 10-14. (canceled)
 15. The brake system according to claim 1,wherein between the actuating device and the second force transmissionmeans a path simulator is arranged, a pedal travel limitation of whichparticularly can be switched off by means of a device. 16-17. (canceled)18. The brake system according to claim 1, wherein between each workingchamber and the associated at least one wheel brake, one or more2/2-directional control valves are arranged.
 19. The brake systemaccording to claim 1, wherein through corresponding triggering of thedrive device the brake system sets necessary servo braking and pressuremodulation for ABS and/or ESP function.
 20. The brake system accordingto claim 4, wherein the second force transmission means comprises aclutch plunger against the piston and wherein the spherical bushing issecured against rotation particularly by means of a form-fit.
 21. Thebrake system according to claim 20, wherein the securing againstrotation takes place by at least one ball track, which extends into arespective adjacent recess. 22-23. (canceled)
 24. A method for testingthe operation of the brake system according to claim 1, wherein throughcomparison of possible pedal and spindle travel by adjusting the pistonthe operation of the clutch can be tested.
 25. The method according toclaim 24, wherein the operation of the clutch is diagnosed in that thefirst force transmission means is moved into the starting position bythe drive device against the immobilised second force transmissionmeans, so that this operates a clutch plunger relative to the firstforce transmission means and thereby disengages the clutch,serviceability of the clutch being determined if the first forcetransmission means can be moved further than a coupling path.